The restoration of teeth commonly involves the use of (meth)acrylate-based free-radically polymerizable resins that can be chemically cured or light cured. Chemical curing typically involves a redox system with a peroxide oxidizing agent and an amine reducing agent that produces free radicals that initiate polymerization. Light curing typically involves a photoinitiator system that produces free radicals upon exposure to light (400-1000 nm) Photoinitiator systems also have been used in conjunction with cationically cured dental compositions, for example epoxy-based resins, that are cured by way of a cationic ring-opening polymerization curing mechanism. For example, ternary photoinitiator systems comprising an iodonium salt, a visible light absorber (e.g., CPQ), and an electron donor (e.g., a polycyclic aromatic) have been utilized for curing both free-radically cured (meth)acrylate resins and cationically cured epoxy resins.
Many (meth)acrylate-based composite dental restoratives employ ethyl 4-dimethylamino benzoate (EDMAB) as an electron donor in the photo initiator system. Although EDMAB provides good curing properties, dental composite compositions using EDMAB usually require the addition of UV stabilizers, such as benzotriazole derivatives (e.g., TINUVIN P), to achieve adequate color stability. Color stability is an important property for dental restorative compositions since it can impact the long term aesthetics of restorations made from the composition. Many amine electron donors, such as EDMAB, that are used in dental photo initiator systems are susceptible to color formation as a result of photo oxidation processes that occur after curing of the restorative. The addition of a UV stabilizer to the composition helps to prevent this color formation. Unfortunately, UV stabilizers can reduce the fluorescence of the restorative. Since natural teeth fluoresce when irradiated with UV light, restoratives that lack natural tooth fluorescence, for example, because of the presence of a UV stabilizer, will become more noticeable, and thus less aesthetically pleasing, when viewed under UV radiation or “black light” conditions.